At present, the effluents of irradiated nuclear fuel reprocessing plants and technological effluents of nuclear power stations are treated in an industrial evaporation tower, i.e. a plate column in which distillation takes place under reduced pressure. Such a procedure makes it possible to deplete effluents having a low .alpha. concentration, i.e. for the C.E.A. (COMMISSARIAT A L'ENERGIE ATOMIQUE) centre at VALDUC, effluents having a contamination in .alpha. elements below 1.5.10.sup.7 Bq/m.sup.3 and in saline charge below 50 g/l. This gives a concentrate containing virtually all the .alpha. activity and a saline charge of approximately 300 g/l. This concentrate is treated and subsequently conditioned in concrete. This procedure also makes it possible to bring evaporates consisting of 90% of the aqueous phase of the treated effluents to an activity of 300 to 500 Bq/m.sup.3, i.e. well below the discharge value permitted at present (1000 Bq/m.sup.3). This procedure has hitherto permitted the discharge of these effluents into the environment following monitoring of the toxic, radiological and chemical elements.
However, as from 1994, the new standards imposed with respect to the discharge into the environment of effluents have become much more strict. Thus, for the Valduc C.E.A. centre, any effluent discharge must have a maximum .alpha. contamination of 1 Bq/m.sup.3. Therefore, said effluents must be completely purified in order to bring about a "zero" discharge into the environment.
The existing evaporation procedure does not make it possible to satisfy the new discharge standard, because it is not possible to eliminate the phenomenon of entraining .alpha. contamination to the vapour. Therefore this procedure is not sufficiently effective and leads to the obtaining of very slightly charged solutions with a radioactive activity between 200 and 300 Bq.alpha./m.sup.3 (below 1000 Bq.alpha./m.sup.3).
It is therefore necessary to develop complexing agents permitting the treatment of evaporates from industrial evaporation towers in order to eliminate the final traces of .alpha. emitting elements. In addition, these complexing agents could also be used for treating effluents upstream of the industrial evaporation tower, so as to be able to optionally replace the latter, whilst still obtaining effluents having activity levels in accordance with the new environmental discharge standards.
The prior art discloses macrocyclic compounds having excellent complexing properties with respect to cations, anions or even neutral molecules. Thus, FR 2 643 370 in the name of Air Liquide describes derivatives of the following general formula: ##STR1## in which A, B, C and D can represent --(CH.sub.2).sub.x --, x being between 1 and 4 and W, X, Y and Z representing=N--(CH.sub.2).sub.y --COR, y being between 1 and 4 and R representing an OH, NH.sub.2 or OR' group. These derivatives can be used as complexing agents of metallic elements and in complexed form as oxygen traps.
However, these macrocyclic derivatives are generally highly soluble in water. Therefore the use, recovery and regeneration of said derivatives in solution are not very easy. For these reasons, several fixing methods have been developed in order to graft these macrocyclic derivatives to organic or inorganic supports which are not soluble in water. Thus, U.S. Pat. No. 4,943,375 discloses a macrocycle grafted on silica usable in a separation column for trapping a given ion present in a solution of several ions.
French patent application 2 613 718 describes cyclic tetramines grafted on a polymer and usable for the selective extraction and/or dosing of ions of transition metals and heavy metals. However, these grafted macrocycles suffer from the disadvantage of not being selective of a particular type of metals.
In the nuclear sector, European patent application 347 315 describes a process for separating, by means of crown ethers, uranium and plutonium present in an aqueous fuel resulting from the reprocessing of irradiated nuclear fuels. The crown ether can be DCH 18C6, DCH 24C8 or DB 18C6.
There are a priori numerous applications for said modified polymers, such as e.g. the trapping of metallic elements contained in effluents, the purification of organic solvents contaminated by various cations produced in the electronics industry (cf. C. Pong, "Polymer material for electronic applications", E. D. Felt, C. W. Wilkin, Eds: ACS Symposium Series 184, American Chemical Society, Washing D.C., 1982, pp 171-183) or the use of silica gels modified by copper complexes in liquid phase chromatography (cf. M. A. Bagnoud, W. Haerdi, J. L. Veuthey, Chromatographia, 1990, 29, (9/10) pp 495-499). A particularly interesting application relates to the selective coordination properties of gaseous molecules (O.sub.2, CO.sub.2) of a certain number of complexes formed by these macromolecules with Co(II), Fe(II), Mn(II), Cu(II), etc.
During the last decade a novel dioxygen production process has been developed. Using as a basis natural dioxygen transportation systems (hemoglobin, hemocyanin), it is performed in solution. This process essentially uses Co.sup.II, Fe.sup.II, and Cu.sup.II complexes of tetraazamacrocycles, Schiff bases or porphyrins. The latter selectively fix dioxygen from the air and the desorption stage can be performed electrochemically. This process in solution is usually limited by the life of the oxygenated complexes, which are subject to irreversible degradation reactions by acid hydrolysis in order to form inert complexes no longer having an affinity for dioxygen.
However, it has been demonstrated that the grafting of complexes able to coordinate dioxygen on organic or inorganic, solid matrixes would make it possible to cancel out the decomposition process observed in solution, cf. e.g. the article by J. P. Collman et al, J. Am. Chem. Soc., 1973, 95, 2048 or the article by J. H. Fuhrhop et al, J. Macromol. Sci. Chem., 1979, Al3, 545. Moreover, a sufficiently low concentration of grafted complexes adequately moves away the metal centres to prevent any formation of binuclear species. The choice of a relatively hydrophobic polymer reduces the water content of the matrix and therefore the hydrolysis of the oxygenated complex.
The invention aims at removing the disadvantages of the prior art.